The present invention relates generally to hacksaws, and specifically to hacksaws that can effectively mount high speed blades requiring a lesser tension and bimetal blades requiring a much higher tension in the blade.
There recently have become available bimetal blades for hacksaws which require substantially higher tensions for effective operation than the standard high speed blades for hacksaws generally used heretofore, the bimetal blades requiring tensions on the order of 40,000 p.s.i. Hacksaw constructions available heretofore have not offered sufficient mechanical advantage in the blade tensioning mechanism to provide tensions of this order of magnitude.
The prior blade tensioning mechanisms for hacksaws are illustrated by the Keymer U.S. Pat. No. 3,636,997 granted Jan. 25, 1972. In this patent, the lever 78 forms a portion of the handle 14 and is used to apply tension to the blade 26. The lever 78 does not give a high tension in the blade, but rather permits the blade to be placed in either a tensioned or untensioned condition, there being no suggestion of progressively tensioning the blade in order to obtain a high mechanical advantage and resultant capability of high tension in the blade.
Other patents showing cranks and levers in the blade tensioning mechanism are the Glenn U.S. Pat. No. 2,725,911 granted Dec. 6, 1955, the Lorusso U.S. Pat. No. 2,034,625 granted Mar. 17, 1936 and the Thompson U.S. Pat. No. 1,446,674 granted Feb. 27, 1923. None of these patents show a progressive tensioning of the blades so as to achieve high tensions therein.
Patents showing progressive tensioning of the hacksaw blade are the Dreier U.S. Pat. No. 2,796,098 granted June 18, 1957, the Dreier U.S. Pat. No. 2,808,086 granted Oct. 1, 1957 and the Dreier U.S. Pat. No. 2,869,600 granted Jan. 20, 1959. Each of these patents shows the use of a knurled knob in order to apply tension to the hacksaw blade. The knurled knobs illustrated do not provide sufficient mechanical advantage adequately to tension blades such as bimetal blades to the required operating tension.
Furthermore, none of the patents noted above have any means for indicating the tension applied to the hacksaw blade. This is important when utilizing different types of hacksaw blades requiring different tensions, thus to ensure that the proper tension is applied to each blade encountered during the use of the hacksaw.